1. Field of the Invention
The present invention relates to a short-range wireless communication device such as a wireless USB (Universal Serial Bus).
2. Description of the Related Art
Along with progress in the wireless technology, cable connection in the related art is more and more replaced by radio connection. For example, in the related art, a LAN (Local Area Network) is primarily connected using an Ethernet, typically, the IEEE 802.3 (the Institute of Electrical and Electronic Engineers 802.3) system. However, recently, more and more information communication apparatuses are typically connected using the IEEE 802.11 wireless LAN standard.
This is true not only for LANs, but also for PANs (Personal Area Network) for close range communications. A USB is a typical example. At the present time, since the USB can be used to configure an inexpensive and stable PAN, usage of the USB is widely spread. In order to further improve convenience of usage of the USB, a wireless USB is more and more required. It is expected that because of its characteristics, the wireless USB will be more and more in demand in the audio and video fields in the future.
A TDMA (Time Division Multiple Access) scheme is used in communication through the wireless USB. It is well-known that the TDMA scheme is used in a PHS (Personal Handy phone System). In the TDMA used for the PHS, however, since the time slot is fixed, if the data rate decreases due to errors, it is difficult to maintain QoS (Quality of Service). Thus, if the TDMA scheme used in the PHS is applied to the communication through the wireless USB, the communication quality may degrade. This is because the communication through the wireless USB is different from the audio communication (phone call) in the PHS, and it is expected that a large variety of applications requiring a large capacity and real-time QoS will be involved in communications through the wireless USB.
In the above-mentioned wireless LAN system, the concept of QoS is introduced in the IEEE 802.11e standard to ensure a transmission rate. This technique is disclosed, for example, in Japanese Laid-open Patent Application No. 2005-252897 (hereinafter, referred to as “reference 1”), and Japanese Laid-open Patent Application No. 2004-512705 (hereinafter, referred to as “reference 2”). In the communications through the wireless USB, however, the technique of ensuring the QoS is not yet established.
The communication through the wireless USB is performed in a super-frame.
FIG. 1 is a data diagram illustrating a configuration of a super-frame for the communication through the wireless USB.
As shown in FIG. 1, a super-frame is a time interval of 65 ms, which includes 256 MASs (Media Access Slot), each MAS being an elementary unit of a beacon period and a communication time slot. During the communication through the wireless USB, an arbitrary number of the MASs are occupied by the communication to constitute a DRP (Distributed Reservation Protocol), and data transmission and reception are carried out within the “communication-occupied period”. For example, Japanese Laid-open Patent Application No. 2004-364257 (hereinafter, referred to as “reference 3”) discloses a technique for efficiently allocating the DRP. The technique in reference 3, however, is related to mediation between applications at an upper level, which applications use the wireless USB, and this technique cannot meet the requirements of the QoS.
Japanese Laid-open Patent Application No. 11-146454 (hereinafter, referred to as “reference 4”) discloses a digital wireless communication system able to prevent communication failure caused by a busy state of a connection between a main phone and a cordless phone.
As described above, in the communications through the wireless USB, the technique of ensuring the QoS is not yet established, and it is difficult to carry out stable communications. In addition, most devices used in the communications through the wireless USB are driven by batteries, and thus it is desirable to reduce power consumption of devices used in the wireless USB communication system.